The criminal justice system is the largest mental health provider in the U.S., and many jurisdictions are interested in reducing the use of the justice system for behavioral health issues. This 5-year R01 evaluates whether the Stepping Up Initiative overcomes barriers to implementation of EBPPs and the impact on key outcomes, such as increased number of clients receiving behavioral health services, increased use of EBPPs, and dedicated resources to advance the use of EBPPs. The study uses the CJ Evidence-Based Interagency Implementation Model (CJ-IIM) and draws on both quantitative and qualitative methods to understand which dissemination and implementation (D/I) change processes positively impact the expanded use of EBPPs in CJ. Now is an opportune moment, given that 455 counties have agreed to be part of Stepping Up. Mechanisms of interest are: 1) Use of and capacity for performance monitoring to guide system reform and development; 2) Use and functioning of interagency teams; 3) Having common goals and mission across agencies that support system-wide practices to advance the use of behavioral health services for CJS-involved individuals; and, 4) System integration (i.e., building an integrated system of care rather than adding one program or training). The study will survey 455 Stepping Up counties and 455 matched paired target counties (4 respondents per county including administrators of jail, probation, mental health services, and substance abuse treatment services for 3,640 respondents) at three waves: baseline, 18 months, and 36 months. Qualitative interviews will be conducted with 90 respondents at three waves to contextualize survey findings. Stepping Up and comparison counties will be compared on rates of change in engagement of target mechanisms (primary) and rates of change in implementation effectiveness outcomes (secondary) and describe reform activities occurring over a 36-month period. Specific aims are to compare Stepping Up and comparison counties on: 1) Target mechanisms including whether: (a) Stepping Up counties show a faster rate of improvement in hypothesized target mechanisms between Wave 1 and subsequent assessments (i.e., Waves 2 and 3); and (b) whether engagement of these mechanisms explains any differences found in key implementation outcomes; 2) Examine implementation outcomes such as the number of justice-involved clients served with EBPPs, number of behavioral health EBPPs available to justice-involved individuals, and resources for behavioral health EBPPs for justice-involved individuals; and, 3) Characterize implementation processes and critical incidents. We will use qualitative data to triangulate quantitative findings and enrich an understanding of how the target mechanisms work and lead to outcomes, and explore naturally occurring implementation strategies used in 910 counties that lead to outcomes. The study will advance D/I science by contributing to an understanding of 1) systemic decision-making processes in multiple systems with varied goals; and 2) how D/I efforts can target and drive policy and practice reforms.